1. Field
The present disclosure relates generally to composing a computer-generated scene based on perceptual constrains, and more specifically to determining a minimum and maximum value for a bounding parameter based on ocular divergence and convergence constraints.
2. Related Art
Cinematographic-quality computer animation has evolved to produce increasingly realistic and engaging visual effects. One way that this is accomplished is through the use of stereoscopic filming techniques that simulate human binocular vision by presenting slightly different viewpoints of a scene to a viewer's left and right eye. This technique, also known colloquially as “3D,” can be used to enhance the illusion of depth perception and make objects in a computer-generated scene appear to extend outward from a two-dimensional screen.
In normal human binocular vision, each eye views the world from a slightly different perspective. The difference in the view from each eye, also called parallax, is caused, in part, by the spatial separation between the eyes. The brain is able to combine the different views from each eye and use the parallax between views to perceive the relative depth of real-world objects.
Computer animation stereoscopic filming techniques take advantage of the brain's ability to judge depth through parallax by presenting separate images to each eye. Each image depicts a computer-generated object from a slightly different viewpoint. The distance between the left and right images displayed on a screen (parallax) indicates the relative depth of the displayed computer-generated object. Parallax can be positive or negative depending on whether the computer-generated object appears to be behind the screen (positive parallax) or if it appears to be in front of the screen (negative parallax).
In the real world, a viewer's eyes typically focus on a point on an object at a distance from the viewer. The distance from the viewer to the point of focus is also called the focal length. The viewer's eyes may also rotate inward to converge on the same point. The distance from the viewer to the intersection of the optical path of the left and right eye (convergence point) is also called the convergence distance. In normal human binocular vision, the focal distance and the convergence distance are approximately the same. However, displaying a stereoscopic image of an object with left and right viewpoints (separated by a parallax distance), creates a disparity between the focal distance and the convergence distance. The focal distance is essentially fixed as the distance to the screen, while the convergence distance is either in front of or behind the screen, depending on the amount of parallax for an object in the stereoscopic image.
This disparity between focal length and convergence distance may cause problems if the disparity is too large. With respect to stereoscopically filmed images, there are perceptual constraints on the amount of convergence or divergence of the viewer's eyes given the fixed focal length to the display screen. Exceeding these perceptual constraints may cause discomfort for the viewer or result in a pair of images that cannot be resolved to produce a satisfactory three-dimensional effect.
In computer animation, the expected amount of convergence/divergence is determined by a number of interrelated stereoscopic parameters (scene parameters), as discussed in more detail below. Traditionally, the values of many of the scene parameters are fixed or only allowed to vary within a range of hard limits. The fixed values or hard limits serve as a rule-of-thumb for editors and directors, but do not guarantee that the perceptual constraints will be satisfied. Additionally, limiting the scene parameters to a fixed value or fixed range of values may under-utilize the design space when composing a computer-generated scene. That is, fixed ranges limit the ability to make trade-offs between the interrelated scene parameter, which may limit the ability to produce dynamic three-dimensional effects.
The systems and methods described herein provide techniques for computing a range of values for a selected scene parameter that satisfy perceptual constraints.